1. Field of the Invention
The present invention relates to a heat transfer surface capable of transferring heat by phase-converting liquids which are brought into contact with outer surfaces of its planar plate or heat-transfer tube, and more particularly, to a heat exchange wall for use in a evaporator or radiator.
2. Description of the Prior Art
There have been heretofore proposed a number of techniques as to a heat transfer surface for enhancing boiling or evaporating heat transfer.
It has been proposed to roughen the heat transfer surface by sintering, radiation-melting or edging methods to form a porous layer thereon. The wall having such a porous layer is known to exhibit better heat transfer characteristic than that of a conventional planar wall. However, in such a porous layer, since voids or cells formed therein are small, impurities contained in boiling liquid or non-boiling liquid contained therein will enter into the voids or cells to clog them so that the heat transfer performance of the wall will be degraded. Also, since the voids or cells formed in the porous layer are non-uniform in size or dimension, the heat transfer performance is locally changed.
On the other hand, as shown in U.S. Pat. No. 4,060,125 or U.S. Pat. No. Re. 30,077, there has been known a heat exchange wall having a number of tunnels or voids formed under its surface layer and a number of openings allowing the tunnels or voids to open to the outside of the heat transfer surface. Such a heat transfer surface possesses a high heat transfer performance. The openings are larger in size than those of the porous layer obtained through the sintering method, and in the wall having the tunnels and openings a possible degradation in performance due to clogging of impurity, non-boiling liquid and the like is small.
However, the heat transfer surface having the tunnels or voids and the openings requires an optimum openings diameter in compliance with a thermal load imposed to the heat transfer surface. Therefore, when the thermal load is excessively small or large, its heat transfer performance will be degraded.